1. Field of the Invention
The present invention relates to a dry-etching apparatus to be used for manufacturing electronic devices such as semiconductor devices.
2. Description of the Related Art
Recently, along with an increase of integration of semiconductor devices, dry-etching technology is becoming important basic art to the manufacturing of electronic devices.
A conventional planar (parallel electrode) type dry-etching apparatus has a problem that plasma density in the reaction gas is of low level. For example, in a dry-etching of silicon oxide film, the conventional planar type configuration cannot achieve a high enough etching rate, and it is inefficient in productivity.
For the reason as described above, as a means for resolving the problem, a report has been made on the development of a magnetron dry-etching apparatus. [Extended Abstracts (The 34th Spring Meeting, 1987), The Japan Society of Applied Physics and Related Societies, page 455]
Referring now to the operating principle of the conventional magnetron dry-etching apparatus, a reaction gas is provided under fixed pressure in an etching chamber and R.F. power (Radio Frequency electromagnetic wave power) is supplied into the etching chamber. The, the reaction gas is excited into a plasma gas. When a magnetic field is applied to the plasma gas, the electrons are trapped by and move by revolving along the magnetic flux.
Therefore, the path length of electrons increases on account of the revolving motion. Accordingly, collisions of electrons with neutral reaction gas atoms or molecules increase, thereby increasing the plasma density. The etching rate can be greatly increased by the increase of the plasma density in comparison with the planar type dry-etching apparatus.
Thus, the magnetron dry-etching apparatus has an advantage of increasing the etching rate through an increase of plasma density. But, the problem in the magnetron dry-etching apparatus is difficulty of uniform application of the magnetic field on a workpiece substrate. Therefore, the conventionally made devices have a problem that the etching cannot be made uniformly.
Recently, a way of making a uniform magnetic field on a principal face of an object substrate has been provided. This is accomplished by installing a permanent magnet of concentrical polarization. The permanent magnet is rotated behind an anode electrode in an etching chamber, in a manner so as to be rotated by a motor in eccentric manner along an axis offset from its center.
FIG. 1a and FIG. 1b are each views showing the arrangement of the conventional permanent magnet.
FIG. 1c is a graph showing the distribution of etching rates on workpiece substrates, taking pressures in the etching chamber as a parameter, of the workpiece substrates etched by the eccentrically driven permanent magnet shown in FIG. 1a and FIG. 1b. The etching is carried out under the following conditions.
Reaction gas: CHF.sub.3 45 sccm : O.sub.2 5 sccm PA0 R.F. power: 450 W PA0 Workpiece substrate: silicon oxide film on a silicon wafer of 6 inch diameter
The results shown in FIG. 1c are obtained under the following conditions: Under 50 mtorr in an etching chamber, the eccentric position for rotation of the permanent magnet is adjusted so that it provides a uniform etching rate on the surface of a workpiece substrate. However, it is apparent from FIG. 1c that: etching rates are different between a central part and peripheral parts of the wafer, corresponding to local changes of pressure in the etching chamber. Therefore, it will be understood that uniform etching rates cannot be obtained under pressures of 20 mtorr to 100 mtorr.
FIG. 2a, FIG. 2b, and FIG. 2c schematically show the state of plasma discharge by stopping the permanent magnets shown in FIG. 1a and FIG. 1b. The shaded portions in FIG. 2 are regions of high level plasma density. In the figure, it will be understood that regions of high level plasma density are displaced from peripheral parts toward the center of the wafer as the pressure in the etching chamber increases. This is an important reason for irregular or nonuniform etching due to nonuniformity of plasma density caused by change of pressure.
For the reasons as described above and shown in FIG. 1c, in the conventional configuration of the permanent magnet, distribution of plasma density is much different from one position to another position of the wafer, and the difference (nonuniformity) changes as the etching conditions change, especially as the pressure changes. As a result, whenever the etching conditions are changed, it is necessary to adjust for uniformity of etching rate by changing the arrangement of the permanent magnet, or by readjusting the axis of rotation.
Accordingly, it is the primary object of this invention to provide a dry-etching apparatus which can provide etching with excellent uniformity without any need of adjustment of the permanent magnet arrangement even when the etching conditions are changed. The above object of the present invention is achieved by an improved magnetron dry-etching apparatus which has a specially polarized permanent magnet member with rotation means behind an anode electrode. The special disposition of the permanent magnet is such that plural pairs of oppositely polarized narrow-pie-shaped permanent magnets are disposed in a circular or fan shape. Respective narrow-pie-shaped permanent magnets are disposed by arranging their straight sides adjacent to each other along a radius of the circle; and so on. The poles of the permanent magnets are arranged such that oppositely polarized poles, i.e. N-pole and S-pole form a unit pair disposed side by side along a radii of the circle with their opposite faces connected to a common yoke.
The magnetron etching apparatus in accordance with the present invention 1 comprises:
an etching chamber containing a cathode electrode for placing a workpiece substrate thereon, 100 l. 13 . PA1 an anode electrode installed in parallel arrangement to the cathode electrode with 5 gap inbetween, 0.1 1/10,000 PA1 means for applying R.F. power across the cathode electrode and the anode electrode, PA1 means for supplying reaction gas to the etching chamber, and PA1 means for evacuating the etching chamber to predetermined pressure, PA1 a permanent magnet assembly located behind the anode electrode and having means for rotation in a plane parallel to the anode electrode and comprising at least a pair of narrow-pie-shaped permanent magnets fixed to a yoke in a manner such that different polarity magnetic poles are disposed side by side on both sides of a radial line originating from the center of the rotation, with apexes or apices of the narrow-pie-shaped permanent magnets at the center.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.